Low-Resolution ADCs for Two-Hop Massive MIMO Relay System under Rician Channels

This paper works on building an effective massive multi-input multi-output (MIMO) relay system by increasing the achievable sum rate and energy efficiency. First, we design a two-hop massive MIMO relay system instead of a one-hop system to shorten the distance and create a Line-of-Sight (LOS) path between relays. Second, we apply Rician channels between relays in this system. Third, we apply low-resolution Analog-to-Digital Converters (ADCs) at both relays to quantize signals, and apply Amplify-and-Forward (AF) and Maximum Ratio Combining (MRC) to the processed signal at relay R1 and relay R2 correspondingly. Fourth, we use higher-order statistics to derive the closed-form expression of the achievable sum rate. Fifth, we derive the power scaling law and achieve the asymptotic expressions under different power scales. Last, we validate the correctness of theoretical analysis with numerical simulation results and show the superiority of the two-hop relay system over the one-hop relay system. From both closed-form expressions and simulation results, we discover that the two-hop system has a higher achievable sum rate than the one-hop system. Besides, the energy efficiency in the two-hop system is higher than the one-hop system. Moreover, in the two-hop system, when quantization bits q=4, the achievable sum rate converges. Therefore, deploying low-resolution ADCs can improve the energy efficiency and achieve a fairly considerable achievable sum rate.

Low-Resolution ADCs for Two-Hop Massive MIMO Relay System under Rician Channel

Advantages of the system in this PaperThis paper investigates the uplink of a two-hop massive Multi-input Multi-output (MIMO) relaying system with low-resolution Analog-to-Digital Converters (ADCs) at both relays. Significantly different from previous work, we design a two-hop MIMO system to shorten the distance between each hop, so that there will be Line-of-Sight (LOS) path between relays. This allows signals to be transmitted under Rician channels instead of Rayleigh channels and thus increases the sum achievable rate. Second, we apply low-resolution ADCs at both relays of the system to reduce the energy burden. The main work of this paperThe main work of this paper is as follows. First, assuming the Channel State Information (CSI) is perfect, we use the higher-order statistics to derive the closed-form expression of the uplink sum achievable rate of the two-hop low-resolution ADCs massive MIMO relay system under one-hop Rayleigh channels and two-hop Rician channels. Next, supposing that the number of antennas tends to infinity, we derive the law of power scaling and further achieve the asymptotic closed-form expressions and the asymptotic values under different power scales. Next, we verify the correctness of theoretical analysis with numerical simulation results, and compare the results under one-hop Rayleigh channels and two-hop Rician channels. Finally, we conclude that transmitting signal under two-hop Rician channels can achieve a lower sum achievable rate compared with transmitting under one-hop Rayleigh channels, which means it's more effective to apply two-hop Rician MIMO system. Besides, we conclude that deploying low-cost and energy-efficient low-resolution ADCs at a large-scale relay system can improve the energy efficiency and achieve a fairly considerable sum achievable rate at the same time.